GERMINATION AND GROWTH 



45 



" peg " ; can you tell its use? Could the cotyledons get out 

 of their hard covering without it? Slip the peg below the 

 coat in one of your growing specimens, leave it in the soil, 

 and see what will happen. How do the cotyledons of the 

 squash differ from those of the bean as they come out of the 

 seed cover? Do they act as foliage leaves? Do you see 

 any difference in the development of the plumule in the two 

 seeds (Figs. 19, 25) to account for the different behavior of 

 the cotyledons? Sketch three seedlings in different stages, 

 labeling correctly the parts observed. Make a similar study 

 of the castor bean, or other seedling selected by your teacher, 

 and illustrate by drawings. 



44. Arched and straight hypocotyls. — This difference in 

 the manner of getting above ground is an important one. 

 That by means of the arched hypocotyl is, in general, charac- 

 teristic of the process of germination in which the cotyledons 

 come above ground, while the straight kind, which was illus- 

 trated in the corn and wheat, is the prevail- 

 ing method when the cotyledons remain 

 below ground. Can you give a reason for 

 the difference ? 



45. Polycotyledons ; germination of the 

 pine. — Examine a pine seedling just begin- 

 ning to sprout. What part emerges first 

 from the seed coat? Where does it break 

 through ? Where did 3^ou find the micropyle 

 in the pine seed? (15.) Can you give a 

 reason why the hypocotyl in seeds should 

 break through the coats at this point ? How 

 do the cotyledons get out of the testa? Is 

 the hypocotyl arched or straight in germination? How does 

 it compare with the bean and s(|uash in this respect? With 

 the corn ? Is any endosperm left in the testa after the cotyle- 

 dons have come out? What has become of it? Do the 

 cotyledons function as leaves ? How many of them has the 

 specimen you are studying ? Notice the little knob or button 



60. — Pine 

 scodliim (Aftii- ( iRAY). 



